PVC membrane based potentiometric sensors for uranium determination

Two novel uranyl PVC matrix membrane sensors responsive to uranyl ion are described. The first sensor incorporates tris(2-ethylhexyl)phosphate (TEHP) as both electroactive material and plasticizer and sodium tetraphenylborate (NaTPB) as an ion discriminator. The sensor displays a rapid and linear response for UO22+ ions over the concentration range 1 x 10(-1)-2 x 10(-5) mol l(-1) UO22+ with a cationic slope of 25.0 +/- 0.2 mV decade(-1). The working pH range is 2.8-3.6 and the life span is 4 weeks. The second sensor contains O-(1,2-dihydro-2-oxo-1-pyridyl)-N,N,N ' ,N ' -bis(tetra-methylene)uronium hexafluorophosphate (TPTU) as a sensing material, sodium tetraphenylborate as an ion discriminator and dioctyl phenylphosphonate (DOPP) as a plasticizer. Linear and stable response for 1 x 10(-1)-5 x 10(-5) mol l(-1) UO22+ with near-Nernstian slope of 27.5 +/- 0.2 mV decade(-1) are obtained. The working pH range is 2.5-3.5 and the life span of the sensor is 6 weeks. Interference from many inorganic cations is negligible for both sensors. However, interference caused by some ions (e.g. Th4+, Cu2+, Fe3+) is eliminated by a prior ion exchange or solvent extraction step. Direct potentiometric determination of as little as 5 mug ml(-1) uranium in aqueous solutions shows an average recovery of 97.2 +/- 1.3%. Application for the determination of uranium at levels of 0.01-1 wt.% in naturally occurring and certified ores gives results with good correlation with data obtained by X-ray fluorescence. (C) 2001 Elsevier Science B.V. All rights reserved.